Today we use the Gregorian calendar, which was invented some time after the birth of Jesus.
In order to clarify our thinking we usually extrapolate (or extend) our Gregorian system back to historical times, that is, we calculate what dates would have been had they been using our calendar in their day.
In 1 BC people were not huddled around their fireside at night wondering what was going to happen at the end of the year. They had their own calendar.
Jesus's Birth
Our year number, for example, 2007, is based on Jesus supposedly having been born at a point in time, 0 (zero) (note; not a year number, but a point in time).
The "year AD 2007" lasts from Jan 1, 2007 until Dec 31, 2007, the latter date being 2007 years after Jesus's birth ( !! ).
Jesus was probably not born on January 1st, and he was born some years before the point in time 0 (zero). Hence our prefix or suffix "AD" has very little to do with the actual time when Jesus was born.
Henceforth we will take 0 (zero) time to be only an historical convention and we will not refer to Jesus's birth again in this article.
Numbering the Years
-3 -2 -1 0 1 2 3
-I--------I--------I--------I--------I--------I--------I-
year 3BC 2 BC 1 BC AD 1 AD 2 AD 3
The upper row of numbers, -3 to 3, represent yearly POINTS IN TIME, and they all existed, every one of them.
The lower row, 3 BC to AD 3, are the historical NAMES OF THE YEARS.
So, someone going away on business 1.5 years before 0 (zero), and returning 1.5 years after 0 (zero), would, in history, be described as leaving in 2 BC and returning in AD 2.
Therefore in history the businessman would appear to have been away 4 years if we were to blindly add 2 and 2. We properly should allow for the absence of a year NAMED ZERO between the years named 1 BC and AD 1.
created 22jan07